Surface light source device of side light type

Abstract

In a surface light source device of side light type applied to a liquid crystal display or the like, particularly, a surface light source device of side light type with emitting directivity, irregularities in luminance of output light are prevented from occurring in the vicinity of an incidence surface. In a surface light source device of side light type 10, a diffusible area M1 to diffusely reflect illumination light and an absorptive area (on a reflection sheet 11) to restrain the illumination light from reflection from bands in the vicinity of the incidence surface oppositely with the emitting surface of a light guide plate 12 with emitting directivity. It is thereby possible to reduce irregularities in output light luminance occurring in the vicinity of the incidence surface T. A light reflection member 18 may be arranged so as to extend over an edge EU of the emitting surface of the light guide plate 12, with directivity of illumination light emitted from the the emitting surface being modified. A light blocking material may be arranged on a side end surface of a light control member 13 to prevent illumination light emitted from a light source from being directly incident. Illumination light incident on the edge EU of the light guide plate may be blocked by a light blocking member 18. The diffusible area may be formed by roughening a surface opposite with the emitting surface.

What is claimed is: 
     
       1. A surface light source device of side light type, which deflects illumination light incident through a side end surface of a light guide plate to emit said illumination light from an emitting surface of said light guide plate, comprising: a combination consisting of a band-like diffusible area to diffusely reflect said illumination light and a band-like absorptive area to restrain said illumination light from reflection from bands in the vicinity of said side end surface oppositely with said emitting surface of said light guide plate, wherein said combination includes a blurred boundary area formed so that a difference between said diffusible area, said absorptive area and the rest of said light guide plate is substantially undetectable by an observer.   
     
     
       2. A surface light source device of side light type according to claim 1, further comprising: a light reflection member arranged so as to extend over an edge at which said side end surface and said emitting surface of said light guide plate meet;   a light control member to modify directivity of the illumination light emitted from said light guide plate arranged on the side of said emitting surface; and   a light blocking material arranged on a side end surface of said light control member, so that said illumination light emitted from said light source is prevented by said light blocking material from being directly incident on said light control member.   
     
     
       3. A surface light source device of side light type according to claim 1, wherein said illumination light incident on the edge adjacent of said side end surface of said light guide plate is blocked by a light blocking member, further comprising a light control member to modify directivity of the illumination light emitted from said light guide plate and arranged on the side of said emitting surface and receiving part of said illumination light emitted from said light source directly. 
     
     
       4. A surface light source device of side light type according to claim 1, 2 or 3, wherein said diffusible area is formed by roughening said surface opposite to said emitting surface. 
     
     
       5. A surface light source device of side light type according to claim 1, 2 or 3, further comprising a reflection sheet to reflect said illumination light leaking out through said light guide plate, and arranged on the side of the surface opposite to said emitting surface and wherein said absorptive area is formed by adhering a light absorptive substance to an area on said reflection sheet. 
     
     
       6. A surface light source device of side light type according to claim 4, further comprising a reflection sheet to reflect said illumination light leaking out through said light guide plate, and arranged on the side of the surface opposite to said emitting surface and wherein said absorptive area is formed by adhering a light absorptive substance to an area on said reflection sheet.